The first objective of these studies is to analyze the organization of nucleus laminaris in the barn owl. The brainstem nucleus laminaris is the first site of binaural interactions in the barn owl, and is also where sensitivity first appears to the interaural temporal disparities which underlie sound localization. The analysis of temporally ordered inputs is integral to information processing in the brain, and mechanisms underlying this process may be particularly accessible in nucleus laminaris. The cellular mechanisms of sound localization in nucleus laminaris will be investigated using ultrastructural techniques. Afferents from cochlear nucleus magnocellularis interdigitate in nucleus laminaris to create a map of interaural temporal disparities. Regulation of conduction velocity in these afferents may provide the precise timing observed; to this end we will measure morphological correlates of conduction. Magnocellularis afferents converge upon neurons of nucleus laminaris which are hypothesized to act as coincidence detectors. Ultrastructural analysis of these neurons will provide a description of their synaptic organization and cellular properties. How is the map of delays in nucleus laminaris assembled during development, and subsequently turned? The normal development of nucleus magnocellularis and nucleus laminaris will be studied until the end of the sensitive period (two months old), at which time the head reaches adult dimensions and the owl experiences stable sound localization cues. The development of the afferent delay lines and the neurons of nucleus laminaris will be analyzed during the time the system is subject to changing sensory cues.